JPH07107948B2 - Non-coherent optical non-coupling laser array - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a non-coherent, non-phase-locked laser array, and particularly to a high intensity, uniform far-field radiation distribution over a wide range, and an electro-optical line. It relates to a non-phase-locked or optically non-coupled laser array which is very suitable for use as a light source for a modulator and an electro-optical line printer.

(Prior Art) In the prior art, semiconductor lasers and LEDs have been used as light sources that produce images on photosensitive media such as xerographic photoreceptors used in xerographic printers. In such applications, the light intensity of the image must be uniform and the intensity of the emitted light must be sufficient. Also, when LEDs have to be used, a full width array of LEDs is provided, one for each pixel or pixel, so that a row of light is formed and the photoreceptors can be neutralized according to the image. There is a need.
Generally, a plurality of light emitting element (LED) arrays are arranged in one or more rows and an optical means is positioned between the photosensitive medium and the light source array to direct light from each array light source onto the surface of the photosensitive medium. It converges on a single line. Then, each light source is selectively turned on / off to perform line-by-line exposure of the moving photosensitive medium.

Since the semiconductor laser also has high intensity at the focused spot,
It has been used as a light source for rotating polygon scanning printers and the like. However, these semiconductor lasers are not optimal for use in electro-optical line printers because of insufficient power and inadequate uniformity of light intensity. In particular, a high power, coherent laser source has a far-field emission distribution that includes high-intensity regions and low-intensity regions in a single beam in the far region. That is, the far-field radiation distribution is not uniform. Such a transverse intensity variation of the beam output is undesirable because the linewise exposure on the photosensitive medium is not uniform. For the above and other reasons, LEDs are more preferred as the light source for electro-optical line printers because they can be designed to have a monotonically varying light output with a very short coherence length.

However, in some cases, conventional LEDs have not been able to provide sufficient output power and intensity to efficiently perform the function of exposing a charged, moving photosensitive medium. Also, LEDs are much less efficient than lasers. For this reason, LEDs used as light sources in xerographic photoreceptor applications lack sufficient output intensity levels for good photoreceptor removal, and as a result, semiconductor lasers are often the preferred light source for printer applications. It is said that it is preferable.

In addition to the problem of insufficient LED strength, multiple L
Ensuring uniform light output between each of the ED and multi-laser light sources is also recognized as a problem in the art. To ensure that the intensity of the broad light emission from the LED array is uniform across the array, a sophisticated control system, such as that illustrated in U.S. Pat.No. 4,455,562, provides a uniform light intensity distribution. Has been designed to give. The above patents utilize binary weighted duty cycle control to obtain a substantial uniformity of the light emitted from each LED in an LED array.

The highest power LEDs are top emitter, but still lack the power intensity needed for most printer applications. That is, a sufficient light density cannot be obtained per aperture size.

(Problems to be Solved by the Invention) The most recent advance in the printer field is total internal reflection (TI
R) The concept of line modulator, which is a solid-state multi-gate light valve used to address photosensitive media. A TIR line modulator consists of a crystal bar of electro-optical material, on one of its main faces an array of comb-like electrodes is deposited, which when electrically addressed causes these electrodes to be periodic in the crystal body. Generates or induces an electric field. Each electrode is individually addressed by an electrical signal that forms a signal pattern across the array. Line modulators require a high intensity, wide sheet light beam. The beam is introduced to the crystal at a constant angle of incidence in the plane of the major surface with the electrodes. An example of a TIR line modulator is Robert A. Sprang
Ue et al., U.S. Pat. No. 4,281,904.

In order to carry out the exposure process of the photosensitive medium, the sheet-shaped light beam is incident through the electro-optical element of the TIR line modulator at a slight angle with respect to the optical axis of the light,
Internal total reflection occurs on the inner surface provided with electrodes. Successive sets of digital bits or analog samples representing respective collections of pixels or pixels contained in successive lines of the image are sequentially applied to the electrode array. A local body or peripheral electric field generated in the crystal in proximity to the TIR incident light modulates the light, causing the phase front of the sheet of light beam to change on the charged photosensitive medium depending on the shape of the image. Examples and teachings for applications of electro-optical line printers are provided in U.S. Patent Nos. 4,367,925; 4369,457; 4,370,029; 4,437,106; 4,
450,459; 4,480,899 and 4,483,596.

More recently, for electro-optic line modulators and line printers, a superluminescent LED side light source with high output intensity and uniform far-field distribution, and tangential (transverse) direction parallelization of the far-field radiation have been developed. And optical means have been developed to focus the near field radiation in the sagittal (front-back) direction on the modulator. The optical means includes a first lens system that collects light emitted from the LED light source in both tangential and sagittal directions,
A second toric lens for collimating the light in the tangential direction to the sheet-like beam and converging the light in the sagittal direction into a line image on the modulator. Imaging means are optically aligned between the modulator and the recording medium to image the modulator onto the recording medium of the line printer. Regarding this point, refer to JP-A-61-232686.

LEDs with such multi-gate or electro-optic modulators allow printers to have a monotonically varying emission distribution in a wide and predictable manner without the sharp or irregular structures found in diode laser arrays. It has almost ideal characteristics as a light source for applications. Moreover, the light spectrum of the LED is wide enough to neglect the light interference effect. However, because LED light is emitted in many different directions, LEDs have lower overall efficiency, such as conversion efficiency, than diode lasers due to their inherent properties, so LEDs of comparable output power have higher temperatures than diode laser sources. And need to operate with high input power.

That is, a light source that combines the noncoherence of an LED with the efficiency of a diode laser is desirable in line modulator and printer applications.

(Means for Solving the Problems) According to the present invention, a non-coherent diode laser array light source is used as a single solid-state light source that is sheet-shaped, uniform, and can be provided with high intensity. Consists of an array of diode lasers that are closely spaced but not coupled to each other. What is important is that the individual lasers or radiators of the laser array operate in random phase with respect to each other, i.e., they are sufficiently dissipated that their phases are not coupled to each other. That is, if each laser in the array oscillates independently of the other lasers, its optical phase and / or frequency will drift randomly resulting in the individual beams of the diode lasers rather than between the beams of adjacent diode lasers in the array. Allows optical interference to occur only within each laser.

To fabricate an array of closely spaced lasers operating on an optically uncoupled method on a single chip, the intensity of the extinction region extending from each laser cavity to an adjacent laser cavity must be , Should be reduced below the level required to achieve stable phase lock. This decoupling can be done in several ways. For example, first
In a typical array of gain-guided lasers, individual laser elements can be separated by a relatively long distance to obtain decoupled operation.
For example, they should be separated by about 50 μm or more. However, separating the laser elements in the array by a very large distance reduces efficiency by increasing the wasted light that spreads out from the active area of the individual laser elements, and may also increase distance for certain applications such as electro-optic modulators and line printers. It becomes impossible to collect the light of the area efficiently. In addition, the large separation reduces the overlap of the far-field distributions of the individual laser emitters, resulting in non-uniform far-field distribution across the array, and thus such structures are not suitable for electro-optical line printers. On the other hand, in the case of an array of index-guided lasers,
The far-field separation problem is better satisfied because the light fields provided by the individual lasers of the array are tightly confined so that the emitters of the individual lasers do not need to be separated as much. In both the index-guided type and the gain-guided type laser array, light absorption can be performed between the lasers in order to remove light leakage from one laser into the waveguide portion or cavity of the adjacent laser. There is an increase in the threshold and a decrease in efficiency. Therefore, closely coupled and uncoupled arrays that do not include light absorption are most desirable.

The present inventors have developed a method of uncoupling lasing by tilting individual laser emitters or using impurity-induced disordering (II D) to form isolation regions between the laser cavities of the array. It is proposed to provide the required close spacing between each laser emitter of the array while maintaining operation. The desired purpose is to isolate the optical cavities of the individual lasers so that optical coupling does not occur between them.

Other objects and advantages besides the above, together with a fuller understanding of the invention, will become apparent from the following detailed description and claims taken in conjunction with the accompanying drawings.

EXAMPLES Referring to FIGS. 1 and 2, an electro-optical line printer 11 with a peripherally responsive multi-gate light valve or TIR line modulator 12 for printing an image on a photosensitive recording medium 13. Is shown. Recording medium as shown
13 is a photoconductive coating drum 14 which is rotated (by means not shown) in the direction of arrow 13A. However, it will be apparent that other xerographic and non-xerographic recording media can be used including photoconductive coated belts and plates as well as photosensitive films and coated papers and the like. Therefore, the recording medium 13 in the generalized case should be exemplified as a photosensitive medium that is exposed while being advanced in the cross line or line pitch direction with respect to the modulator 12.

As shown most clearly in FIGS. 3 and 4, modulator 12
Comprises an optically transparent electro-optical element 17 and a plurality of individually addressable electrodes 18A-18I. The most promising electro-optic material for such devices is Li
NbO ₃ and LiTaO _3, but DSN, KDP, KdxP, Ba ₂ NaNb ₅ O ₁₅ and PLZT
Other materials, including, are also worth considering. In this particular embodiment, modulator 12 operates in TIR mode. That is, the electro-optical element 17 is preferably a y-cut crystal of LiNbO ₃ , for example, and has an optically polished reflective surface 21 extending between the opposite optically polished entrance and exit surfaces 22, 23, respectively. Generally, each electrode 18A-18I is 1-30 microns wide and the gap between the electrodes is also 1-30 microns.

When the operation of the modulator 12 is briefly examined with reference to FIGS. 1 to 4, the sheet-like collimated light beam 24 from the non-coherent laser array light source 15 is incident on the optical system 16 and the electro-optical element 17 at the front end. The light travels through the surface 22 at a glaze incident angle with respect to the reflecting surface 21, that is, an angle smaller than the critical incident angle required for total internal reflection from the reflecting surface.

The incident beam 24 is laterally spread by the optical system 15 so as to irradiate the electro-optical element 17 substantially uniformly over its entire width, and the optical system 16 also causes the incident beam 24 to be distributed substantially at the center of the electro-optical element 15. It is focused on the wedge-shaped focal point 24A on the reflecting surface 21 of. Therefore, the incident beam 24 is totally internally reflected from the reflecting surface 21, and is emitted from the electro-optical element 17 to its emitting surface 23.
An outgoing beam 25 is provided which exits through.

The phase plane, or polarization, of outgoing beam 25 is spatially modulated in response to the data applied to electrodes 18A-18I. That is, when the data causes a voltage drop across any adjacent pair of electrodes, such as electrodes 18B and 18C, the corresponding peripheral field is coupled to the electro-optical element 17 causing a local change in its refractive index. To efficiently couple such a peripheral field to the electro-optical element 17, the electrodes 18A-18I are supported on or in close proximity to the reflective surface of the element 17. Electrode 18a
The ~ 18I is preferably deposited on a suitable substrate such as a VLSI silicon circuit 28, which is pressed or otherwise held tightly against the electro-optical element 17 as indicated by arrows 28 and 30. And keep each electrode 18A-18I in contact with, or at least in close proximity to, the reflective surface 21. The advantage of this structure is that the VLSI silicon circuit 28 can be used to make the necessary electrical connections to each of the electrodes 18A-18I. Alternatively, the electrodes 18A to 18I are formed on the reflecting surface 17 of the electro-optical element 17.
May be attached.

For purposes of illustration, the phase plane of exit beam 25 will be at each electrode 18A-18I.
Shall be spatially modulated according to the data applied to the. Therefore, in order to convert the modulation of the phase plane of the outgoing beam 25 into a corresponding modulated intensity distribution and to give the surface of the recording medium 13 a magnification necessary to obtain an image of a desired size,
Schlieren's central dark or bright field imaging optics are used. That is, as shown in the figure, a central dark area image forming optical system 31 including a field lens 34, a central stopper 35, and an image forming lens 36 is provided. The field lens 34 is optically aligned between the exit surface 23 of the electro-optical element 17 and the central stop 35 and focuses substantially all of the 0th order diffracted component of the incident beam 25 on the central stop 35. But,
The higher order diffractive components of the exit beam 25 bypass the stopper 35 and are scattered and collected by the imaging lens 36,
36 converges them and the higher-order diffracted components on the recording medium 13 to give an intensity-modulated image of the modulator 12.

Referring again to FIG. 4, note that each electrode 18A-18I is individually addressable. Thus, to print the image, differently coded data samples for each successive line of the image are sequentially applied to each electrode 18A-18I. The definitional problem is that, except for the first sample for each line of the image, each differently coded data sample will be differently coded earlier by an amount corresponding to the size of the particular input data sample. It has a size different from that of the liquefied sample. The first differently coded samples for each line are standardized to a predetermined potential such as ground. Thus, when differently coded data samples for any line of the image are applied to each electrode 18A-18I, the pixels for that line will be faithful to the electrode-to-electrode voltage drop in modulator 12. Represented by.

To provide differently coded data samples, serial input data samples representing adjacent pixels or pixels for successive lines of the image are applied to the differential encoder at a predetermined data rate. The encoder differentially encodes the input samples line by line, and the multiplexer multiplexes each electrode at a ripple rate that matches the data rate.
Give ripple to coded data samples on 18A-18I. The input data may be buffered to match the input data rate to any desired rate.

Alternatively, a set of ground plane electrodes (not shown, but defined as electrodes standardized to the same voltage level as the raw input data sample) are interleaved with the individually addressable electrodes and require differential encoding. Can also be removed. However, as a general principle, the advantage of reducing the number of electrodes required to achieve a given resolution outweighs the disadvantage of providing the additional circuitry required for differential encoding.

In the printer 11, the optical system 16 is, for example, in the sagittal direction,
The near-field light from the laser array light source, which is a spot 1/4 to 1 micron wide, is imaged onto modulator 12. This spot image is reduced by the modulator 12 to the width of one diffraction limited spot. The exit beam 25 from modulator 12 is then expanded into a 10 micron spot for a 1 micron source spot. In the tangential direction, the light is collimated towards the modulator 12 by the optics 16 so that the modulator 12 is illuminated in the far field of the laser array light source 15.

Thus, the electrodes of each adjacent pair such as the electrodes 18B and 18C shown in FIG. 4 cooperate with the electro-optical element 17 and the read-out optical system 31 to effectively limit the local modulator and reproduce it on the recording medium 13. Pixels or pixels are formed at unique, spatially predetermined locations along each line of the image to be formed.

An example of the optical system 16 for collimating and converging the sheet-like beam 24 on the surface of the modulator 12 to the wedge-shaped line 24A is shown in Japanese Patent Laid-Open No. 61-232686.

Next, a laser array of a type suitable for use in the line printer 11 will be described. In general, the radiators of a laser array must not be phase locked, but must be closely spaced enough so that the far pattern is a uniform Gaussian radiation pattern. Corresponds to the far-field radiation pattern of an individual laser emitter or each laser element of the array. That is, the spatial reference of the radiators must be close enough in space so that they form a uniform far-field pattern, but at the same time do not give a phase lock between adjacent radiators. Must be This is a difficult condition because phase locking occurs when the radiators are closely spaced, as evidenced by the prior art.
On the contrary, when the separation between the radiators is increased to the extent that the stable phase lock is removed, the distance between the radiators becomes large and the far-field radiation distribution becomes non-uniform, and the lobe and far-field radiation distribution lobe and The unevenness remains and prevents the uniformity in the direction across the far-field distribution.

Thus, while the radiators are spaced sufficiently close together, they are not phase locked or noncoherent with respect to each other and the net light intensity in the far range is the result of adding the light intensity of the individual radiators. It is necessary to introduce some mechanism or means to do so. This mechanism or means may be provided in the form of lateral deviations in the geometry of each radiator, or in the form of isolations interposed between the individual radiators in a refractive index guided laser array structure. An example of lateral displacement of the radiator is shown in FIG. 5 and an example of optical isolation is shown in FIG.

FIG. 5 illustrates a non-coherent laser array 40 having a plurality of closely spaced laser elements formed by implementing a geometrically offset geometry of the laser elements. The individual radiators in FIG. 5 are optically decoupled in the array by virtue of the vertical and lateral offsets of each laser element and are therefore not phase locked. The structure of the laser array 40 comprises a substrate 42 of, for example, n-GaAs, which is selectively etched in a conventional manner to provide a periodic structure 43 of alternating mesas 45 and channels 47. Next, a metal-organic chemical vapor deposition (MO-CVD) growth method is used to form the semiconductor layer 4
Epitaxially grow 4 to 48. Each of these layers associated with the laser structure includes a cladding layer 44 of n-Ga _1-x Al _x As (where x is 0.4); and an active layer which may be a single active layer or a single quantum well structure or a multi-quantum well structure. Region 46 and; n−Ga
A cladding layer 48 of _1-x Al _x As (where x is 0.4) and a cap layer 50 of p ⁺ -GaAs. The laser array 40 has individual radiators 54
A proton or ion implant suitable for confining high current in the region of G, and also G-Au or Ti-Pt on the cap layer 50.
An -Au metallization layer 56 and an Au-Ge alloy layer may also be provided, after which a Cr-Au or Ti-Pt-Au metallization layer 52 is provided on the bottom surface of the substrate 42.

Individual laser emitters 54 in this non-planar array
Lateral separation of the non-planar radiator array because the vertical light field of each radiator is confined very tightly by the strong optical waveguides formed by the periodic structure 43 and penetrating each layer 44-48. Can be made smaller compared to. For example, if the lateral displacement between the laser cavities represented by the radiator 54 is 2 to 3 μm, it is suitable to avoid optical coupling between the adjacent laser elements, and the distance between the laser cavities is smaller than that of the planar type array. Allows close lateral or horizontal spacing. Also, the closer spacing of the laser array 40 using the geometric offset allows the pumping current applied to the array to be used more efficiently. The minimum lateral separation of the laser emitter depends on the vertical plane separation, but can be smaller than 10 μm.

FIG. 6 shows a non-coherent laser array 60 formed by impurity-induced disordering (II D) having a plurality of closely spaced laser elements. Only three laser emitters 78 for convenience and simplicity
, But it is clear that more radiators can be formed.

The laser array 60 consists of a substrate 62 of n-GaAs on which the following layers are epitaxially deposited: n-Ga _1-x Al _x
A cladding layer 64 of As (x equals, for example, 0.4) with a layer thickness of about 1.5 μm; separated by a single active layer or a single quantum well structure or, for example, a Ga _0.65 Al _0.35 As barrier layer each 7 nm thick. Active region 66 composed of four GaAs quantum well layers each having a thickness of 10 nm; p-Ga
_1-x Al _x As clad layer 68 (x equals 0.4, for example) 68
And the p ⁺ -GaAs layer 7 has a layer thickness of about 0.8 μm; and a layer thickness of about 0.1 μm.
0. The active region may be p-doped, n-doped or undoped.

After forming an array of diffusion windows on the Si ₃ N ₄ film deposited on the cap layer 70 to form the II Dn type region 72 shown in FIG. A silicon film is deposited. The processing steps of the laser array 60 begin with the deposition of a 100 nm thick Si ₃ N ₄ film. This film is photolithographically patterned to provide windows or openings for forming regions 72 by Si diffusion. next,
After depositing about 50 nm thick silicon film on the array, about 100 n
Another the Si ₃ N ₄ film of m thickness is deposited. Diffusion is carried out at 850 ° C. for 7.5 hours to finally disorder the active region in the area adjacent to the portion which will be the lasing filament represented by 78 in the figure.

The n-type Si diffusion region is shown as the shaded region 72 extending through the active region 66. The diffusion region preferably extends through the active layer and any other layer that forms or functions as part of the optical cavity of each laser element. In this regard, the diffusion is best partly extended into the lower cladding layer 64, depending on, for example, the proportion of aluminum in the inner cladding layer. If the additional inner confinement layers comprise active regions, the diffusion preferably extends through the confinement layers as they are also part of the optical cavity of the laser element. The result to be achieved is that the diffusion must extend through the optical cavities of each laser element enough to prevent a stable phase lock between adjacent cavities due to the overlap of dissipative light waves extending between adjacent cavities. There is something that must be done. The diffusion region 72 provides optical confinement of the dissipative light waves, as well as carrier confinement for the individual laser cavities represented by the radiators 78, so that the individual laser elements are not optically coupled to each other and may range from about 4 to The center-to-center distance of 10 μm makes it possible to closely arrange them closely.

After diffusion, the Si layer and both Si ₃ N ₄ layers are removed by etching in CF ₄ plasma. Next, as shown by the cross-hatched area 74, Zn diffusion is performed to reconvert part of the n-type Si-diffused GaAs cap layer 70 and the cladding layer 68 into a p-type layer. Due to the characteristics of the parasitic pn junction 69 parallel to the laser oscillation junction in the active region obtained as a result, it is important that the Zn diffusion penetrates into the cladding layer 68. As a result of Zn diffusion, the parasitic pn junction 69
Is located in the high aluminum cladding layer 68,
It has a much higher on-switching voltage than in the GaAs active region 66. Since the bandgap at the pn junction 69 is significantly higher than the bandgap of the GaAs junction in the active region, the pn junction 69 conducts at a much lower current than the lasing junction in the active region at a certain junction voltage. . Thus, the leakage current through junction 69 in high aluminum is a very small fraction of the total current flowing through the array element and does not significantly degrade element performance.

In addition, after a relatively wide mask is aligned to cover more than halfway between the two diffusion regions 72 on both sides of the device, proton bombardment isolation is performed on the outer regions of the array 60. This isolation is represented by the dotted line in FIG. 6 and forms an isolation region 76. The purpose of this proton injection is
It is to prevent current flow in the outer region 76 which was not previously disordered by the diffusion of silicon. To achieve this, the proton implants need only fall somewhere within the outer Si disordered region, so the alignment of the implant mask is less critical.

After proton implantation at a dose of 3 × 10 ¹⁵ and an energy of 70 keV, the laser array 60 is formed on the gap layer 70 by Cr-Au or Ti-.
After being metallized with Pt-Au and alloyed with Au-Ge,
Cr-Au or Ti-Pt-Au is metallized on the bottom surface of the substrate 62.

Λ on the front of the laser array 60 for passivation
A / 2 Al ₂ O ₃ layer may be applied. Also, in order to increase the reflectance to 95% and reduce the laser oscillation threshold of the device by about 20 to 30%, a multi-layered structure of 6 layers consisting of a pair of Al ₂ O ₃ —Si λ / 4 layers was deposited on the back surface. You may.

It has previously been demonstrated that several different diffusing nuclides can also generate II D disordering effects. For example, Z
Disordering is also possible with n, Ge, Sn and S. Also, Se, Mg, Sn, O, S, Be, Te, SI, Mn, Zn, Cd, Ln which act as impurities at a shallow level or a deep level. ,
It is possible to make disorder by performing high temperature annealing (heat treatment) which is best performed in an As environment after implanting an element such as Cr or Kr.

Dispersion disorder by diffusion of both zinc and silicon has been successfully constructed in laser devices, and the lower threshold ultimately attainable with these devices has been of great interest. Since IID devices have very strong lateral confinement to carriers, the threshold current is mainly limited by the width of the laser contact stripe that can be obtained in the photolithographic process and maintained in the diffusion process. . In the II D laser structure created as described above, the device geometry is such that the contact mask is dimensioned to be smaller than the width of the lasing filament while avoiding contact between the active region and adjacent diffusion regions. Demanded that. Therefore, if a very narrow lasing filament, for example 2 μm wide, is desired for each laser radiator, the width of the lasing stripe is limited by the minimum achievable aperture of the diffusion window and the corresponding alignment tolerance. Will be. This problem is further compounded when it is desirable to make a multi-emitter laser array of the kind in which it is highly desirable to place the emitters in close proximity and without phase locking. However, a novel feature of laser array 60 is that it completely dips the n-type diffusion in the p-type compensation region across the entire width of the array element, allowing the use of a single large area surface contact to pump the entire array. The idea is to do so. Using this technique, it is possible to successfully reduce the width of each radiator to less than about 2 μm with 6 μm spacing between the radiators, resulting in a current threshold of about 53 mA, power output up to 250 mW CW or more, for example. A laser array 60 of 10 radiators with is produced.

(Advantages of the Invention) From the above, the closely spaced separation of the laser oscillation elements in the array is achieved without causing phase lock, that is, optical coupling, and a wide range of uniform distances most suitable for electro-optic modulators and printers is achieved. It will be clear that in addition to being able to produce a regional emission distribution, it can provide a low operating current threshold and lower heat generation compared to LED superluminescent devices of comparable output power.

Some advantages of the non-coherent laser array of the present invention over superluminescent LEDs are as follows:
First, no special lobes appear in the far-field radiation distribution. Secondly, the speckle pattern in the far range is reduced because the effect of addition of different speckle patterns of individual laser elements in the array occurs instead of optical coupling, and the combination effect in the far range is reduced in the far field radiation pattern. Provides a high level of uniform intensity. Third, the current threshold of about 50 mA clearly demonstrates a significant reduction in heating problems. Fourth, the laser array is about 20-40% more efficient than superluminescent LEDs. Fifth, because of its low current / temperature operating characteristics, the laser array provides wide power coverage for different types of electro-optical line modulators and line printer input sources.

7 and 8 show characteristics of power vs. current output, and a multi-radiator having a multi-quantum well structure having a 2-μm wide radiator 78 described above with reference to FIG. 5 and having a spacing between the radiators of 6 μm. 3 shows the near-field and far-field radiation distributions of the laser array 60. The lasing threshold of this array is 53 mA. The pulsed power vs. current curve 80 in FIG. 7 gives a difference quantum efficiency of 62%. If the measured series resistance is 1.3Ω, then 2
The total efficiency of power conversion at 50 mW is 43%. Such a high efficiency value is obtained when the waveguide part of the lasing filament is made of Si.
It has been demonstrated that there is relatively little loss that occurs in the diffusion process of. The near-field radiation pattern shown in the inset of FIG. 7 also reveals a strong lateral optical confinement, as evidenced by the fact that the radiator has a clearly resolved zero separation. . In addition, form an array
Note that the uniformity among the 10 radiators is also high.

In Figure 8, the uniform wide far-field distributions for 100, 150 and 250 mA pulsed operation and 150 mA CW (continuous wave) operation are shown as well matched Gaussian distributions, It is shown that there is non-coherent behavior between the separate radiators that enhances the applied input without causing phase lock. Each radiator 78 may be closely spaced within 6 μm without causing any phase lock condition under different applied currents.

In order to fabricate the laser array having the emission wavelength in the visible region described here, for example, InGaP / InGaAsP / InGaP or AlGaInP
Other alloys such as / InGaP / AlGaInP can also be used.

The doping type of each layer of the laser array is p-type II D region.
In the case of 72, it is obviously reversed. Furthermore, in order to shift the absorption to the high energy side, a transparent window may be formed on the emission surface of the laser array by thermally annealing the quantum well active region on a small region near the laser emission surface.

The present invention has been described above with reference to some characteristic examples.
It will be apparent to those skilled in the art that many substitutions, modifications and variations are possible based on the above description. Accordingly, the present invention is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims.

[Brief description of drawings]

1 is a schematic side view of an electro-optical line printer for carrying out the present invention; FIG. 2 is a plan view of the printer shown in FIG. 1; FIG. 3 is an enlarged side view of a TIR multi-gate line modulator; FIG. 4 is an enlarged bottom view of the modulator shown in FIG.
FIG. 5 shows individually addressable electrodes of the modulator; FIG. 5 is a schematic diagram of a non-coherent laser array used in the printer shown in FIG. 1; FIG. 6 is another diagram used in the printer shown in FIG. Fig. 7 is a schematic diagram of a non-coherent laser array; Fig. 7 is a graph of pulsed and CW (continuous wave) power band current characteristics for the laser array shown in Fig.
FIG. 8 shows a near-field radiation distribution at a drive current of A; and FIG. 8 is a graph of far-field radiation characteristics for the laser array shown in FIG. 11 …… Line printer, 12 …… Electro-optical line modulator, 40,60 …… Noncoherent laser array, 45,47; 72 …… Structural means (45; Mesa, 47; Channel, 72;
Isolation area (diffusion area), 54,78 ... Radiator (laser element).

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Thomas El Paoli, California 94022 Los Altos Cypress Drive 420 (72) Inventor Robert Dee Vernam, California 94306 Palo Alto South Court 2912 (56) Reference U.S. Pat. (US, A)

Claims (4)

[Claims] 1. A non-coherent optically uncoupled laser array, such as for an electro-optical line modulator or line printer, wherein the laser array comprises laser emitters occupying a plurality of spatial locations. The laser has a high power density and a uniform far-field distribution, and is close enough to provide such a uniform far-field distribution without phase locking between adjacent radiators of the laser array. A non-coherent optically uncoupled laser array, characterized in that the laser array is provided with means for allowing the radiators to be spaced apart. 2. A series of laser elements formed spatially close to each other so as to form a far-field radiation distribution of uniform intensity, and a laser element provided between the laser elements and dissipating the laser elements. And non-coherent optically uncoupled laser arrays, the structural means preventing the optical zones from overlapping into the optical cavities of adjacent laser elements to cause phase locking. 3. The non-coherent optically uncoupled laser array of claim 2 wherein said structural means comprises lateral and oblique misalignment of adjacent optical cavities of the laser element. 4. The structure means extends across the laser ray and into the laser array a distance sufficient to optically isolate the optical cavities of the laser elements from each other and prevent optical coupling between adjacent laser elements. The non-coherent optically uncoupled laser array of claim 2 comprising a plurality of extended spatially spaced isolation regions.